1. Field of the Invention
The present invention relates to a semiconductor integrated circuit including a bleeder resistor circuit allowing for external trimming.
2. Description of the Related Art
FIG. 3 is a block diagram of a conventional semiconductor integrated circuit including a trimmable bleeder resistor circuit. The circuit includes a write control circuit 102 having a data input terminal 97 and a clock input terminal 96 as input terminals; a memory 103 composed of plural memory cells to which data are written in response to an output from the write control circuit 102; plural trimming switches 104 composed of MOS transistors switchably turned on/off in accordance with data held in the memory 103; a switch control circuit 106 for transmitting the output from the memory 103 to the trimming switches 104 after buffering; and a bleeder resistor circuit 105 partially trimmed of f by means of the trimming switch 104. The bleeder resistor circuit 105 changes the total resistance value in accordance with the combined use of the trimming switches 104 in an on-state and those in an off-state.
The write control circuit 102 includes a shift register 99 for counting clock signals inputted from the clock input terminal 96; and a data register 100 for temporarily storing trimming data inputted from the data input terminal 97.
In writing data, trimming data to be written are inputted serially to the data input terminal 97 in synchronism with the clock signal inputted to the clock input terminal 96. Once the clock signal reaches a terminal end of the shift register 99 for counting the clock signals, a write signal is outputted to a data write control signal node 98, and trimming data stored in the data register 100 are transmitted to corresponding memory cells in the memory 103.
In reading data, the trimming data stored in the memory cells in the memory 103 are transmitted to the trimming switches 104 by way of the corresponding switch control circuit 106 to thereby turn on/off the corresponding switch.
That is, the bleeder resistor circuit 105 can be trimmed into a desired resistance value by serially inputting to the data input terminal 97 data representing the combined use of the trimming switches 104 in an on-state and those in an off-state, by which a desired resistance value is attained (see JP 2003-242799 A (p. 12, FIG. 1)).
However, with the conventional semiconductor integrated circuit including the trimmable bleeder resistor circuit, the number of flip-flop circuits in the data register 100 increases along with an increase in bit number of trimming data, resulting in a larger layout area. This disadvantageously hinders cost- and size-reduction of the semiconductor integrated circuit.